1. Field of the Invention
The present invention relates generally to a process of manufacturing multi-layer electronic components with electrodes embedded in ceramics, and in particular a process for building multiple layers of ceramics and electrodes using radiation curing techniques to manufacture multi-layer electronic components and products thereof.
2. Description of Related Art
A multi-layer electronic component often contains both conductive and non-conductive layers. It is sometimes required to form inter-layer electrical connections between the conductive layers to produce electronic components with the desired electrical characteristics. There are a few existing processes for manufacturing multi-layer electronic components.
First, there is the dry sheet process (e.g., U.S. Pat. No. 5,032,815). Dry sheets of ceramic green tapes with electrodes printed thereon are used as the basic parts of the electronic components. These ceramic tapes and electrode materials are made of ceramic and metal powder respectively bound together by polymer binders. These dry sheets are laminated at elevated temperatures and high pressure. To allow inter-layer connections, holes are punched on the ceramic tape and filling of metal powder ink in those holes are necessary to form vias. After the structure is formed, a burnout process is required to remove/decompose the binder and a firing process is required to sinter the ceramic powder and metal powder to provide the desired physical and electrical properties. This process involves many steps and many pieces of major equipment (tape casting, tape cutting, via punching, electrode printing, tape peeling, tape stacking, and lamination) to complete the buildup for the component.
For the dry sheet process, sheets and electrodes are dry, thus interlayer solvent interaction will not likely occur during lamination. However, since the location with electrodes is normally thicker than the location without electrodes, higher pressure lamination could cause material creeping. Problems with de-lamination or short circuit for thin layers may occur.
The second process is a semi-wet process (e.g., U.S. Pat. No. 4,322,698). Dry sheets are made for the top and bottom ceramic layers, but a wet process is used to print electrodes and ceramic layers in between. This process involves many process steps and many pieces of major equipment (tape casting, tape cutting, tape peeling, tape pressing, printing for both ceramic and electrode active layers, drying, tape stacking, and tape lamination) to complete the buildup. Solvents are also used in dissolving or dispersing organic binders for binding ceramics and metal powder together to form the desired structure. Drying is required to remove the solvent and solidify the ceramic slurry and metal ink. It consumes a substantial amount of time and heat energy, and is normally not friendly to the environment.
Finally, another existing process is the wet process (e.g., U.S. Pat. No. 5,650,199). A curtain coater or similar devices are used to lay down ceramic coatings in slurry form on pallets or bars to build multilayer ceramic components. Each layer of coating sticks to those above and below it without the need for lamination, which is required in both the dry sheet and semi-wet process. When using a wet buildup process for making an interlayer connection, a dot, made of a metal ink, is printed on top of the electrode, which has been printed on top of a ceramic layer that rests on a pallet, at the location where a connection to the upper adjacent electrode is desired. A thin layer of ceramic slurry coating is then applied on the top of the pallet by using a curtain coater. Due to the chemical-physical incompatibility of the dot ink and ceramic slurry, vias or holes, which are occupied by the dot ink, are formed on the ceramic coating layer.
The wet process requires at least two major steps (coating and printing) and at least three pieces of major equipment (coating, drying, and printing) to complete the buildup process. Compared to the dry sheet and semi-wet processes, the wet process significantly reduces the process steps and labor costs. However, because the layers are generally wet when they are stacked against each other, there is an interaction between the solvents in different layers exists, which can cause an undesirable effect on the electrical performance of the device, hence reducing the yield of the production. Since the curtain coating follows the contour of the prints, it is difficult to obtain flat and even surface. The uneven surface could further affect subsequent printing and via forming.
It is desirable to provide an improved process for forming multi-layer electronic components which overcomes the drawbacks in the prior art.
The present invention overcomes the drawbacks of the prior art by minimizing the use of solvents in the metal ink and ceramics slurry. The binders used are of the type that cures (e.g., by polymerization) by applying radiation, such as UV or electron beam (hereinafter xe2x80x9cE beamxe2x80x9d). According to one embodiment of the present invention, UV light or E beam curable binders are mixed with ceramic powders and metals powders to form ceramic slurry and electrode ink, obviating the need for solvent in the metal ink and ceramic slurry. Instead of drying, a UV or electron beam is used for solidifying the binders. These binders could contain UV/electron beam curable monomers or oligomers, photo initiators, and other additives to provide the desired chemical and physical properties in the forming process. Fewer steps are needed in this process, thereby saving cost and enhancing quality. This process is also more friendly to the environment.